1. Field of the Invention
The present invention relates to a method for producing alkylsulfinylbenzamides and 1,2-benzisothiazol-3-ones. More particularly, the present invention relates to a method for producing alkylsulfinylbenzamides which are useful as intermediates for 1,2-benzisothiazol-3-ones, etc. and a method for producing 1,2-benzisothiazol-3-ones directly from 2-(alkylthio)benzamides. 1,2-benzisothiazol-3-ones are compounds useful as antibacterial agents and antifungal agents.
2. Discussion of the Related Art
The following methods are known for producing alkylsulfinylbenzamides.
(A) Bull. Chem. Soc. Jpn., 55, 1183-1187 (1982) ##STR1## (B) Tetrahedron Lett., 33, 153-156 (1992) ##STR2## PA1 (C) Bull. Chem. Soc. Jpn., 55, 1183-1187 (1982) ##STR3## PA1 (D) Ger. Offen. 3500577 (1986) ##STR4## PA1 (E) J. Org. Chem. 40(14), 2029-2032 (1975) ##STR5## PA1 (1) A method for producing an alkylthiobenzamide represented by the general formula (III), comprising carrying out a reaction of a halobenzamide represented by the following general formula (I): ##STR8## wherein X represents Cl or Br, and R.sup.1 represents a hydrogen atom, or an alkyl group having 1 to 4 carbon atoms, an aryl group, or an aralkyl group,
These conventional methods, however, are not advantageous for industrial use for various reasons. Specifically, Method (A) has problems in stability and production of its starting material, 2-(methylthio)benzoyl chloride. Also, periodic acid, which is expensive and dangerous, is used in this method.
Method (B) has a problem in obtaining the starting material, because no methods have been disclosed for producing the starting material, N-phenyl-2-(methylthio)benzamide. In addition, this method also uses a dangerous substance, m-chloroperbenzoic acid (m-CPBA).
There are also several methods known for producing 1,2-benzisothiazol-3-ones, including the following ones.
In the above method, 2-(methylthio)benzamide is produced from 2-(methylthio)benzoylchloride; oxidized with periodic acid to 2-(methylsulfinyl)benzamide; and cyclized in the presence of thionyl chloride to yield a 1,2-benzisothiazol-3-one.
In the above method, a desired 1,2-benzisothiazol-3-one may be obtained using thiosalicylic acid as a starting material and sodium hydroxide as a cycling agent in the final process.
In the above method, a desired 1,2-benzisothiazol-3-one is obtained using thiosalicylic acid as a starting material and a strong base in the final cyclization process.
However, these conventional methods have the following drawbacks:
In Method (C), a desired 1,2-benzisothiazol-3-one is synthesized in two steps, that is, 2-(methylthio)benzamide is oxidized to 2-(methylsulfinyl)benzamide, which is then cyclized in the presence of thionyl chloride. This method needs use of periodic acid, a dangerous and expensive substance.
Method (D) requires expensive thiosalicylic acid as the starting material, a strong base for cyclization, and involves many reaction steps. Therefore, this method is not satisfactory for industrial use.
Also, Method (E) uses expensive thiosalicylic acid as the starting material and a strong base for cyclization, and involves many reaction steps, and, therefore, is not suitable for industrial use.
As stated above, all known methods require more than one reaction steps to produce 1,2-benzisothiazol-3-ones from 2-(alkylthio)benzamides, and are not satisfactory for production on an industrial scale.